The discrepancy between theory and experiment is larger at \(s=15\,\,{\rm GeV}^2\)  than at \(10.3\,\,{\rm GeV}^2\) .
It seems that the predicted energy dependence is too strong. It also seems that the ratio of the \(\pi ^-\) 
and \(\pi ^+\)  cross sections at \(90^\circ \)  is too large as compared to the Hall A data [1]}.
Some fine tuning of the soft-physics input is perhaps necessary. We however hesitate to do so since
the SLAC data are very old and a remeasurement of wide-angle \(\pi ^\pm \)  photoproduction seems to be advisable.
